The invention relates in general to exhaust guides and more specifically to an apparatus, system and method for guiding an exhaust gas to measure an oxygen concentration.
Oxygen sensors are used to measure the concentration of oxygen in a gas. Many conventional combustion engines utilize oxygen sensors for determining the air to fuel mixture of the exhaust of the combustion engine. Conventional internal combustion engines typically incorporate electronic fueling control using computing devices such as Electronic Control Units (ECU) that meter fuel into the engine intake depending on engine intake airflow. The oxygen sensors are typically mounted within the exhaust system along the engine exhaust gas flow. The exhaust gases flow through an intake of the exhaust sensor exposing a measuring cell within the oxygen sensor to the exhaust gases. The oxygen sensor produces an output signal that indicates the air to fuel ratio of the exhaust gas.
Conventional techniques for measuring exhaust gases, however, are limited in several ways. The exhaust flow within the exhaust system oscillates at least in magnitude and, in some circumstances, also in direction. External air is often sucked back into the exhaust system through the tail pipe. When the oxygen sensor is mounted near the exhaust output, the exhaust gases that are measured are often contaminated by external air which results in an inaccurate oxygen concentration measurement. One attempted solution to this problem includes placing the oxygen sensor or an exhaust guide in the exhaust system away from the exhaust output. If the sensor is permanently mounted within the exhaust system, conventional techniques include modifying a portion of the exhaust system to include a mounting apparatus for the sensor. A typical technique includes cutting an opening within a exhaust pipe and welding a bung within the opening. An oxygen sensor is then screwed into the threaded bung. A significant drawback of this technique includes the extra cost and inconvenience resulting from the exhaust system modification. In addition, the exhaust gases near the engine are often much hotter than near the output. Oxygen sensors mounted near the engine experience high temperatures and well as large temperature variations resulting in deterioration and premature failure of the oxygen sensor. Where the measurement is a performed infrequently, and the presence of the oxygen sensor is temporary, a typical measuring technique includes inserting a long exhaust guide such as pipe into the output of the exhaust system. The long pipe provides the oxygen sensor with exhaust gases that are sampled at a distance form the exhaust opening where contamination from external air is less likely. This technique is limited in that significant measurement delays result from the time required for the sampled gases to travel along the pipe. Changes in oxygen concentration resulting from adjustments and changing engine conditions can not be easily correlated due to the measurement delays.
Therefore, there exists a need for an apparatus, system and method for guiding a gas to a sensing portion of a sensor.